Texture Data UV Coordinates and FBX

Still on vacation in Andalusia, mostly dealing with pretty basic issues and facts of life such as cold rainy weather and a leaking roof, here is another quick post from cold storage:

Question: How can I access the texture data on a Revit model using the Revit API? I am interested in extracting the UV coordinates, colour and texture data on element faces. How can I retrieve the UV texture coordinate information?

I am currently using the FBX SDK to retrieve the texture file name from the texture library. Is this the preferred method? Any samples would be greatly appreciated!

A closely related question came up again recently in an email from Ben Nolan:

Question: I love the Building Coder. But there's a topic you haven't covered – do you know if it's possible to export textures coordinates from within the Revit SDK? We've seen the UVArray class, but can't work out how to get an UVArray from a mesh or other geometry object.

Answer: The Revit API has some ability to extract information about material assets from an RVT file. For example, the following code snippet traverses some of the asset information available in Revit. It can be extended by handling the remaining AssetPropertyType enum cases. It also queries the faces of an element and extracts XYZ information from its triangulation vertices. It attempts to extract some UV information, but that is probably not useful for the texture mapping context:

ElementSet collection = doc.Selection.Elements;
foreach (Autodesk.Revit.Element e in collection)
  String s = "";
  Asset a = e.Category.Material.RenderAppearance;
  for (int index = 0; index < a.Size; index++)
    AssetProperty ap = a[index];
    if (ap.Type == AssetPropertyType.APT_String)
      AssetPropertyString value_str
        = a[index] as AssetPropertyString;

      s += ap.Name + ": " + value_str.Value + "\n";
    if (ap.Type == AssetPropertyType.APT_Boolean)
      AssetPropertyBoolean value_bool
        = a[index] as AssetPropertyBoolean;

      s += ap.Name + ": " + value_bool.Value + "\n";
    if (ap.Type == AssetPropertyType.APT_Float)
      AssetPropertyFloat value_float
        = a[index] as AssetPropertyFloat;

      s += ap.Name + ": " + value_float.Value + "\n";

  Options options = app.Create.NewGeometryOptions();
  options.DetailLevel = Options.DetailLevels.Fine;
  Element geom = e.get_Geometry(options);

  foreach (GeometryObject geomObject in geom.Objects)
    if (geomObject.GetType() == typeof(Mesh))
    else if (geomObject.GetType() == typeof(Solid))
      s = "";
      int nbFace = 0;
      Solid geomSolid = (Solid)geomObject;
      foreach (Face geomFace in geomSolid.Faces)

        Mesh geomMesh = geomFace.Triangulate();
        XYZArray vertices = geomMesh.Vertices;
        int nbVertex = vertices.Size;
        uint indexA = 0; uint indexB = 0; uint indexC = 0;
        for (int i = 0; i < geomMesh.NumTriangles; i++)
          MeshTriangle triangle = geomMesh.get_Triangle(i);
          indexA = triangle.get_Index(0);
          indexB = triangle.get_Index(1);
          indexC = triangle.get_Index(2);

        foreach (EdgeArray geomEdges in geomFace.EdgeLoops)
          foreach (Edge geomEdge in geomEdges)
            foreach (UV geomUV in
              s += "Face: "+ nbFace
                + " UV: " + geomUV.U + " " + geomUV.V + "\n";

It would be nice to be able to directly obtain the UV information something like this, analogously to the XYZ data for the face mesh vertices:

Mesh geomMesh = geomFace.Triangulate();
XYZArray vertices = geomMesh.Vertices;
UVArray uvs = geomMesh.UVs;

However the mesh vertices accessible through the API are the XYZ coordinates of each vertex. The texture mapping is probably defined by the UV coordinates for each vertex that would be calculated if the mesh was unfolded and flattened into a plane. That information is currently not accessible through the API.

There is an alternative approach, though, using the FBX file format.

The FBX format is purpose-built for exchanging information about materials, appearance, and rendering properties. By contrast, the Revit API has only limited ability to extract information about material assets from an RVT file.

The FBX format is consistent amongst other Autodesk products such as Maya and 3DStudio.

In the FBX SDK, the ImportScene sample program might be helpful. You can use it like this:

3DS Max reads and displays the Revit model including all its Mesh, UV information, Material and Texture information. This means that the FBX file has all the required information. The support file assetlibrary_base.fbx probably also includes some library material and texture information.

I removed the comment from the following line 93 in main.cxx:

  FillOwnReaderIOSettings );

Then the sample displays UV coordinates like these:

Mesh Name: Basic Wall kudo [105571]
Control Points
Control Point 0
Coordinates: -47.403542, 16.331938, 0.000000
 . . .
Control Point 7
Coordinates: 33.961288, 17.198078, 0.000000

Polygon 0
Coordinates: -47.403542, 16.331938, 26.246719
Texture UV (on layer 0): 0.000000, 26.246719
Coordinates: -47.403542, 16.331938, 0.000000
Texture UV (on layer 0): 0.000000, 0.000000
Coordinates: 33.961288, 16.331938, 26.246719
Texture UV (on layer 0): 81.364830, 26.246719